In order to comply with state and federal environmental regulations, most motor vehicles are now equipped with a carbon canister installed to trap and store petroleum fuel vapors from the fuel tank. With the canister, fuel vapors are not vented to the atmosphere, but are instead trapped in the canister and then periodically purged from the canister into the engine where they are burned along with the air-fuel mixture.
Typically, a tractive electromagnetic actuator can be used to purge the fuel vapors from the canister. In general, these types of actuators can include a coil, a plunger, a primary plate, a secondary plate, and a frame. The coil can be energized in order to create a magnetic field. The plunger, the primary plate, the secondary plate, and the frame can be used to create a low reluctance path for the magnetic field and to concentrate the magnetic field in certain zones of the magnetic circuit established by the actuator.
It happens that two relatively large reluctances exist in such actuators. For example, a first relatively large reluctance exists between the primary plate and the plunger and a second relatively large reluctance exists between the secondary plate and the plunger. In most cases, the first reluctance varies with the plunger travel. On the other hand, the second reluctance is nearly constant throughout the plunger travel. Since most of the magnetic energy is stored in these two reluctances, or air gaps, it is beneficial to reduce the secondary air gap as much as possible in order to increase the output force of the actuator.
It is a common practice to utilize a thin, non-ferromagnetic spacer, e.g., a very thin walled tube, around the plunger to serve the dual function of spacer and bearing surface for the plunger, while minimizing the secondary air gap. The inclusion of the spacer increases the cost of the actuator by increasing the number of parts within the actuator and increasing the assembly time of the actuator.
The present invention has recognized these prior art drawbacks, and has provided the below-disclosed solutions to one or more of the prior art deficiencies.